Chatting in the fields with growers can bring up many different topics. Invariably these will relate to the inputs, the stage of growth of the crop, the crop type, etc.

Many of these topics are things we can take for granted, but they are still fundamental to the decisions we make in crop production and some are not as well understood as perhaps they should be. So I am jotting down a few remarks about some of the topics that I have been involved in recently.

The whole issue of yield and yield potential came up for discussion while I was standing with a group of farmers in a crop of winter wheat.

The area of yield formation in wheat and barley in particular has received a lot of coverage this year and most growers will not be aware of the basic differences between wheat and barley crops in this regard.

High barley yields are heavily dependent on the creation of high grain counts per square metre and the most effective way to do this is through tiller number rather than ear size.

Wheat is more forgiving and can recover yield potential much later into the growing season. So if the plant count is low, wheat can tiller more profusely.

In low plant populations, a wheat plant can also produce more spikelets per ear on each of the tillers. And at the very end, increased grain fill can be used to make the most of a limiting grain population to generate additional yield.

But how does the plant know how to respond to the environment around it to deliver its potential yield? This is not a simple question and I am not sure that I would know the full answer, but the following points are still relevant.

Yield formation versus yield protection

The vast majority of our chemical inputs are targeted at yield protection rather than yield creation. So our herbicides, growth regulators and fungicides are used mainly to prevent the loss of yield potential.

Some of these may have small positives in terms of improving yield potential, but in the main they protect existing yield potential.

So where does yield potential come from? Why is it that the same pet fields produce the highest yields every year? And, most importantly, what can we do to make all our fields pet fields?

This is obviously a very complex question and any answer is equally complex. However, if you think of things in simple terms, sometimes the answer can appear quite simple. Nitrogen is one of the main yield-generating inputs, but for winter crops this is not always available, depending on conditions through the winter.

During the grass growth stage, a crop is accumulating dry matter and beginning to generate yield potential by creating leaves, tillers, ears, etc. Then it moves on to deliver on the potential yield generated once it moves into stem extension.

Its ability to grow freely generates its yield potential, while after that it is the prevention of a range of stresses which helps to maintain and deliver this yield potential.

While we might not think it, the plant is a living and almost thinking entity. It will do regular, possibly daily or even hourly, audits on its ability to deliver on its full potential and if it feels it cannot do this, it will abort some of the yield sinks (tillers or grain sites) so that the ones which remain can be filled to the optimum degree to ensure its survival.

This is why zero N plots still deliver good grain quality. So every time that the plant feels it cannot deliver (or create) its maximum yield potential, it will reduce its potential.

Can a grower realistically do anything to help this situation? The answer is yes and the key is seen in the pet field.

This is a fertility issue, but it is based on the inherent organic fertility of a field rather than the application of fertilizer. A field with good organic fertility and high humus is better equipped to provide the necessary nutrients for growth whenever growth can take place.

This might only be for a few hours during winter or spring. And based on what I said previously, every growth opportunity which cannot increase yield potential may actually decrease it.

This is the basis behind what happens in a pet field. It is also the basis behind my continuous advice on addressing soil fertility and soil organic matter as these are the major ingredients that make pet fields.

There may be other factors involved, as I have often wondered if growth promotion substances may be released when organic matter is being broken down during the release of nutrients.

Wheel tracks and leather-jackets

During my visit to crops in Armagh last week, there were a number of problems with leather-jackets in fields. Most farmers have the option to spray with chlorpyrifos, but organic farmers do not.

Also, most farmers tend to delay action until they are certain that the damage merits spraying and by then serious plant loss may have taken place.

One trick I came across many years ago may be of interest. Leather-jackets do not generally occur uniformly in a field and so sampling or checking may or may not identify a potential problem. If there is any risk of a problem (in the past this was highest with old ley, but nowadays a problem can occur after a good crop of rape or spring barley) it is much better if leather-jacket activity can be identified before crop emergence.

Many years ago, I stumbled across an interesting and effective monitoring method which happened by mistake. A field of beans was sprayed pre-emerge when soil conditions were marginal. The rear tractor tyres left very marked wheel tracks in the damp soil and these dried out hard in the subsequent dry weather. So the field had a pair of tractor tyre moulds every 12 metres in the seedbed.

This field was actually very bad with leather-jackets (for no good reason). During night-time it is common for the leather-jacket grubs to come above ground to forage for new potential food but they must go back into the soil to avoid desiccation during sunlight hours. As the grubs wriggled across the surface of the ground, they fell into the wheel lug ruts, where they became trapped. Then they were either desiccated or picked up by crows, etc. It is for the same reason that rolling late at night is recommended for leather-jacket control in an effort to seal the ground while the grubs are still on top. If they cannot burrow for protection, they will either be eaten or desiccate.

Either way, they are removed from the field and this damp wheel track technique could be very useful to identify a potential problem.